The field of the present invention is pneumatic mechanisms including reciprocating air driven devices such as air driven diaphragm pumps and valving for such devices.
Pumps having double diaphragms driven by compressed air directed through an actuator valve are well known. Reference is made to U.S. Pat. Nos. 5,213,485; 5,169,296; and 4,247,264; and to U.S. Pat. Nos. Des. 294,946; 294,947; and 275,858. An actuator valve using a feedback control system is disclosed in U.S. Pat. No. 4,549,467. The disclosures of the foregoing patents are incorporated herein by reference.
Common to the aforementioned patents on air driven diaphragm pumps is the presence of two opposed pumping cavities. The pumping cavities each include a pump chamber housing, an air chamber housing and a diaphragm extending fully across the pumping cavity defined by these two housings. Each pump chamber housing includes an inlet check valve and an outlet check valve. A common shaft typically extends into each air chamber housing to attach to the diaphragms therein. An actuator valve receives a supply of pressurized air and operates through a feedback control system to alternately pressurize and vent the air chamber side of each pumping cavity. Feedback to a valve piston is typically provided by the shaft position.
The aforementioned pumps are limited by the magnitude of the inlet air pressure. Even so, such pumps have found great utility in the pumping of many and varied liquids and even powders. Conveniently, shop air is frequently the source of pressure, typically running in the 80 psi to 90 psi range. Naturally, some applications would be advantaged or even made possible by increased pumping pressure. Such applications include long process piping, extremely viscous product pumping, such as automotive paints and paint base compounds, and high compaction filter press operations. Such filter press operations are becoming more and more common with the imposition of stricter environmental regulations requiring the solids in liquid waste to be filtered to a solid waste for safe handling, transportation and disposal. Higher pressures aid in these operations.
A number of enhanced pressure air driven diaphragm pumps are available. These pumps typically rearrange the passages of a conventional air driven diaphragm pump such as described above in a manner that allows one of the two pumping chambers to continue to function in that capacity while the other is used as a further air chamber for magnifying the pumping pressure. To this end, the valves in one of the pump chamber housings are blanked off with a blind seat, plugs or specially constructed chamber. Pressurized air is then introduced to the pump chamber side of the diaphragm in the specially prepared pumping cavity. This pressure is provided at the same time that air pressure is provided to the air chamber side of the unmodified pumping cavity. In this way, a single pumping chamber is provided which is subject to twice the compressive pressure as would otherwise be supplied in a conventional air driven diaphragm pump. However, the ability to pump on each stroke is lost and flow rate is reduced. Such pumps create pressure imbalances with possible components failure.
Pumps employing a single pumping cavity have also been modified with amplified air pressure through the provision of an adjacent cylinder with air pressure alternately provided to opposing sides of an included piston. Air pressure is again provided to the air chamber side of the pumping diaphragm.
Pressure relief valves are also known. Such devices include valve bodies with actuator pins extending therefrom to lift a valve element off of a seat. A flow path through the valve body extends across the valve seat such that flow may be controlled by the valve element which is in turn controlled by the force on the actuator pin. Return springs are used to seat the valve when not lifted from the seat by the actuator pin.
The present invention is directed to relief valves useful with reciprocating air driven devices which can withstand a great number of cycles and operate to provide positive opening characteristics.
In a first separate aspect of the present invention, the relief valve includes a compression spring between the valve element and the actuator. The compression spring accumulates energy to insure a positive opening of the valve with movement of the actuator.
In a second separate aspect of the present invention, the relief valve includes a return spring having the characteristic of an advantageous displacement/force relationship and the ability to withstand a great number of cycles in operation. Installed, the return spring assumes a dome shape and elastomeric material may be employed.
In a third separate aspect of the present invention, the relief valve employs the energy storage capacity of a compression spring with the force transmission characteristics of a solid link in opposition to pressure to provide a positive opening characteristic to a valve element.
In a fourth separate aspect of the present invention, a compression spring between a valve element and an actuator in a relief valve is configured for extended longevity. A block of resilient material is located within a rigid seat to provide the ability to withstand a great number of cycles of the valve without disabling component wear and fatigue failure.
In a fifth separate aspect of the present invention, one or more of the foregoing separate aspects may be combined to positive advantage.
Accordingly, it is an object of the present invention to provide improved pneumatic equipment. Other and further objects and advantages will appear hereinafter.